1. Field of the Invention
The present invention relates to a method of manufacturing an iron member, and to an iron member.
More specifically, the invention relates to a method by which an iron member having excellent anticorrosion characteristics is manufactured with simplicity and ease at low cost under low environmental load conditions, and to an iron member manufactured by such a method.
2. Related Art
As disc brake device for a vehicle, a floating caliper type disc brake is known. In general, the floating caliper type disc brake includes a disc-shaped rotor rotating together with a wheel, a pair of friction pads placed on opposite sides of the rotor, a caliper body to which a piston for pressing one of the friction pads against the rotor is accommodated, and a support member that is mounted on the vehicle body side and supports the caliper body so as to slide in an axial direction of the rotor.
The caliper body includes a bridge part astride the rotor, a cylinder part that is mounted on one end of the bridge part and accommodates the piston in a state of allowing its to-and-fro motion, and caliper claws attached to the other end of the bridge part to hold the back of the other friction pad.
The caliper body and the support member included in the disc brake device are generally made of spheroidal graphite cast iron (FCD450-equivalent material), and the surfaces thereof are given zinc plating and hexavalent chromium-containing chromate treatment, thereby acquiring corrosion resistance.
However, hexavalent chromium remaining in a film formed by chromate treatment sparks fears of detrimental effects on human bodies. In addition, there is a possibility that hexavalent chromium is eluted from chromate-treated wastes and accumulates in the surroundings of its dumping ground.
Therefore, a method of forming chemical conversion treatment film comparable to chromate film currently in use is disclosed (See Patent Document 1), wherein zinc-plated steel bolts are washed with water, given acid activation treatment by immersion in a nitric acid solution or hydrochloric acid solution, further washed with water, and then given a kind of chemical conversion treatment by use of a solution containing a trivalent chromium, molybdic acid and phosphoric acid.
According to the method disclosed in Patent Document 1, however, the zinc plating treatment requires large quantities of washing water, so the method has a problem that not only the treatment process becomes troublesome but also the cost of manufacturing rises due to increases in volume of liquid wastes and footprint of facilities.
[Patent Document 1] JP-A-2000-54157